The suppression or elimination of odors, particularly undesirable odors, has been the objective of countless investigations. Malodors have their genesis in many forms but those that are of most consequence to human beings are those involving occasional or repeated daily exposure. Of primary concern are those malodors that are caused by normal bodily functions, for example, the urine and feces odors associated with infants and the malodors associated with menses.
Cultural and aesthetic standards have influenced the permissible level of human and environmental malodors and control of these odors has been the focus of investigation for many centuries. In general, these investigations have been focused on either of two approaches, namely: (a) odor masking, in which a substance of strong yet relatively pleasant odor is introduced into the proximity of a less pleasant odor source with the intent of overburdening the olfactory receptors with the dominant pleasant odor, or (b) sequestering the undesired odorous substance in a non-volatile form either by chemical reaction, adsorption or absorption on a sorbent material exhibiting a preference for the odorous substance.
Odor masking, although effective in the short term, has certain limitations. First, masking does not remove or eliminate the source of the malodor. Secondly, when scents and perfumes are used to overcome malodors, the user must make sure an effective and constant level of masking agent is present to avoid too low a level of masking agent that may not be sufficient to cover-up the malodor. In turn, too high a level of masking agent may itself produce an undesirable effect. The premature depletion of the masking agent can be an additional concern.
Sequestration has thus become the method of choice for elimination and control of both human and environmental malodors. The more effective approach has been to sequester the undesired malodor primarily by adsorption.
By far the most commonly employed of the solid adsorbents are activated charcoal or active carbon, although silica gel, activated alumina, kieselguhr, Fullers earth and other clay minerals and zeolites, alone or in combination, have also been proposed as odor "adsorbents". In U.S. Pat. No. 4,437,429, to Goldstein et al., issued Mar. 20, 1984, the use of a hydrated zeolite in admixture with clay is proposed as being particularly useful for the control of odors from pet litter. Though it is observed that the use of zeolites by themselves as litter material has generally been unsuccessful due to their poor water adsorption properties as compared with clays. However, these absorbents are direct to methods of soaking up moisture or liquids whereas, described herein below, the present invention is directed to the absorption of volatile substances without the necessity to absorb any liquid carrier material.
The use by women during menstruation of sanitary napkins, pads, and panty liners has become common place. Although natural fluids produced during menstruation are suitably absorbed by the catamenial absorbent material thereby protecting clothing from damage, the problem of malodor persists. This is due in part to the fact that many chemical compounds responsible for malodor typically have very low odor detection thresholds and are perceptible at the part per million (ppm) level. In addition, may of these malodorous materials are hydrophobic easily partitioning out of the liquid phase as the fluids are absorbed by the catmenial substrate material.
It has now been surprisingly found that modified starch granules can be coated with surface modifying agents producing microporous hydrophobic granules that readily absorb malodorous agents even when the agents are in the "gaseous" state. For example, when menstrual fluid is absorbed onto a substrate, volatile low molecular weight compounds nevertheless can still escape into the gas phase resulting in the release of malodors. The modified starch granules of the present invention contain modified surfaces that absorb these and like malodors therefore removing them from the air.
Modification of porous starch granules by partial solubilisation with alpha-amylase for use as dusting powders and talc is described in European Patent Application 182,296, published May 28, 1986. However, the purpose of the modified starch granules is the complete absorption of moisture without concomitant caking.
Other modified starch materials have been described, for example, U.S. Pat. No. 4,985,082 to Whistler, issued Jan. 15, 1991, which discloses treated granular starches derivatized to enhance the absorptive properties. This patent discloses the specific use of interior crosslinking agents to strengthen the granules against collapse when too much moisture is absorbed. This patent relates to releasable containment of an absorbate whereas the present invention preferably does not release the volatile materials once absorbed.